Recently, an article which has a fine uneven structure with a period that is equal to or less than the wavelength of visible light on a surface thereof has been known to exhibit an anti-reflection effect, a lotus effect and the like. In particular, an uneven structure referred to as a moth-eye structure in which convex portions of a substantially conical shape are aligned is known to serve as an effective anti-reflection means since a refractive index continuously increases from the refractive index of air to the refractive index of the material of the article.
As a method of forming a fine uneven structure on a surface of an article, a method of filling a liquid active energy beam-curable resin composition between a mold having a fine uneven structure on a surface thereof and a transparent base material, in which an active energy beam is irradiated thereto to cure the resin composition, and a cured resin layer in which a fine uneven structure is transferred onto a surface of the transparent base material is formed has drawn attention.
As the mold, a mold which has anodized alumina with plural fine pores on a surface of an aluminum base material has drawn attention since simple manufacture is possible (PTL 1).
When a fine uneven structure is formed by anodizing, use of an aluminum base material having surface gloss equal to or more than a predetermined value is disclosed in PTL 2.
The mold is manufactured through a manufacturing method having the following processes (a) to (f).
(a) A process of forming an oxide film by anodizing an aluminum base material in an electrolyte on a surface of the aluminum base material having a high purity which has been subjected to a cutting process.
(b) A process of removing the oxide film by immersing the aluminum base material in a mixture of chromic acid and phosphoric acid after process (a).
(c) A process of forming an oxide film having fine pores by re-anodizing the aluminum base material in the electrolyte after process (b).
(d) A process of increasing the diameter of the fine pores by immersing the aluminum base material in a solution that dissolves the oxide film after process (c).
(e) A process of re-anodizing the aluminum base material in the electrolyte after process (d).
(f) A process of repeating the processes (d) and (e) to obtain a mold in which anodized alumina with a plurality of fine pores having a shape in which the diameter continuously decreases from an opening portion in a depth direction (hereafter, referred as a tapered shape in some cases) is formed on the surface of the aluminum base material.
However, white streaks, which are considered to originate from cutting marks when the aluminum base material is subjected to the cutting process, are easily generated on a surface of the mold obtained by the above manufacturing method on the side where a fine uneven structure is formed. The higher the aluminum purity of the aluminum base material, the more likely it is that white streaks are generated.
When the fine uneven structure of the mold is transferred onto a surface of the transparent base material in a state in which white streaks are present, the white streaks are also transferred onto a surface of the transparent base material. The white streaks look white since white streaks scatter light, and an article with such white streaks transferred onto a surface thereof has high haze and, as a result, visible light transmittance is decreased.
In order to obtain an article (such as an anti-reflective article) with low haze and high visible light transmittance, it is necessary that white streaks not be generated on the surface of the mold on the side where a fine uneven structure is formed, or that the white streaks not be visually recognized, that is, it is necessary to provide a mold with high surface specularity (gloss).